Critical dimension (CD) control is a challenge during semiconductor substrate manufacturing steps such as plasma etching. The uniformity of CD across the substrate can also affect the yield of chips from the substrate. In known semiconductor manufacturing nodes, a CD uniformity of <1 nm can be specified.
Controlling temperature is not an easy task for several reasons. First, many factors can affect heat transfer, such as the locations of heat sources and heat sinks, and the movement, materials and shapes of the media. Second, heat transfer is a dynamic process. Unless the system in question is in heat equilibrium, heat transfer can occur and the temperature profile and heat transfer will change with time. Third, non-equilibrium phenomena, such as plasma, which of course is always present in plasma processing, make the theoretical prediction of heat transfer behavior of any practical plasma processing apparatus very difficult if not impossible.
The substrate temperature profile in a plasma processing apparatus is affected by many factors, such as the plasma density profile, the radio frequency (RF) power profile and the detailed structure of the various heating and cooling elements in the electrostatic chuck assembly, hence the substrate temperature profile is often not uniform and difficult to control with a small number of heating or cooling elements. This deficiency translates to non-uniformity in the processing rate across the whole substrate and non-uniformity in the critical dimension of the device dies on the substrate.
In known plasma processing systems, control electronics for the electrostatic chuck system having one or more thermal control elements such as heaters or peltier devices, can be sensitive to RF noise. As a result, the control electronics are isolated from the active RF of the plasma processing by being located outside of the processing chamber. That is, in known systems the control electronics for the substrate support assembly are located on a high voltage side of an RF filter at a position that is outside the plasma processing chamber. The electrostatic chuck control electronics, on the other hand, are on the low RF voltage side of the RF filter. This arrangement is known to reduce the RF voltage on the ESC heater power lines to levels that do not interfere with the control electronics. When the number of power lines is small (e.g., less than 8-10 power lines), such as for a substrate support assembly having a single temperature control element, the RF filter can be of relatively small size and expense. However, for an electrostatic chuck system having multiple thermal control elements, the number of power lines between the switching control electronics and the electrostatic chuck assembly can be much greater than 8-10 lines (e.g., 16 or 28 pairs of wires), and the RF filter can become prohibitively bulky and expensive. The size, cost, and complexity in RF filtering for electrostatic chuck systems present limitations and problems in the design of electrostatic chuck systems and plasma processing chambers with very tight control on process uniformity (e.g. <1 nm variation in CD).